TWI641558B - System for recovering struvite from wastewater - Google Patents

Abstract

The invention discloses a system for separating and recovering struvite from sewage, which comprises an electrochemical reaction unit, a disturbance unit, a circulation conveying unit and a collecting unit. The electrochemical reaction unit comprises a double-layer reaction tank and an electrode assembly. The double-layer reaction tank comprises an inner tank and an outer tank surrounding the inner tank, and the electrode assembly is disposed in the inner tank. When the double-layer reaction tank contains sewage, The electrode assembly can perform an electrochemical reaction in the inner tank and generate a solid product of struvite in the outer tank; the disturbance unit is used to disturb the sewage in the outer tank to prevent precipitation of the solid product of struvite; the collecting unit passes through the circulating conveying unit Interconnected with the outer tank, wherein the circulating conveying unit is configured to circulate the sewage between the electrochemical reaction unit and the collecting unit, and to settle the high-purity struvite solid product in the collecting unit.

Description

System for separating and recovering struvite from sewage

The invention relates to a domestic sewage treatment system, in particular to a system for separating and recovering struvite from sewage.

Phosphorus resources are non-renewable resources and will be depleted in the middle of this century. Phosphorus resources are mainly used in the food industry (which accounts for the majority) and the national defense industry. When the phosphorus resources are scarce, the food supply will be seriously affected. In addition, the global phosphorus resources are unevenly distributed, so in order to realize the recycling of phosphorus resources, from the sewage. Recycling phosphorus is the primary task at this stage.

Based on various advantages, struvite (magnesium ammonium phosphate) is recognized as the most promising phosphorus recovery pathway, for example, when the solution contains Mg ²⁺ , NH ⁴⁺ , H _n PO ^n-3 and its ion concentration When the product is larger than the solubility product constant of struvite, it will spontaneously precipitate to form struvite. The reaction formula is as follows: Mg ²⁺ + PO ₄ ^3- + NH ₄ ⁺ + 6H ₂ O → MgNH ₄ PH ₄ ‧6H ₂ O;Mg ²⁺ +HPO ₄ ^2- +NH ₄ ⁺ +6H ₂ O→MgNH ₄ PH ₄ ‧6H ₂ O+H ⁺ ;Mg ²⁺ +H ₂ PO ₄ ^3- +NH ₄ ⁺ +6H ₂ O→ MgNH ₄ PO ₄ ‧6H ₂ O+2H ⁺ . The recovered struvite can be used directly as a slow release fertilizer or used in fertilizer production.

In the prior art, the patent application No. CN12167434A discloses a technical solution for recovering struvite from urine by adding magnesium salt, and the patent application No. EP2005/053291 discloses a method of adding precipitant to recover bird droppings from waste mixed wastewater. The technical solution of the stone, the patent CN103732546B discloses a technical solution for recovering struvite from urine using seawater as a magnesium source. Although these technical solutions can handle various wastewaters, However, there are also disadvantages such as high processing cost, difficulty in handling, inconvenient operation and maintenance, low removal efficiency, and low recovery purity.

The technical problem to be solved by the present invention is to provide a system for separating and recovering struvite from sewage by electrochemical precipitation method for the deficiencies of the prior art, which can effectively improve the purity of the recovered struvite for subsequent utilization.

In order to solve the above technical problems, the technical solution adopted by the present invention is: a system for separating and recovering struvite from sewage, comprising an electrochemical reaction unit, a disturbance unit, a circulation conveying unit and a collecting unit. The electrochemical reaction unit comprises a double-layer reaction tank and an electrode assembly, the double-layer reaction tank includes an inner tank and an outer tank surrounding the inner tank, and the electrode assembly is disposed in the inner tank, wherein the double layer When the reaction tank contains sewage, the electrode assembly can perform an electrochemical reaction in the inner tank and generate a solid product of struvite in the outer tank; the disturbance unit is used to disturb the sewage in the outer tank to avoid the Precipitating the struvite solid product; the collecting unit is interconnected with the outer tank through the circulating conveying unit, wherein the circulating conveying unit is configured to circulate the sewage between the electrochemical reaction unit and the collecting unit, and The struvite solid product settles in the collection unit.

Further, the bottom of the inner groove is separated from the bottom of the outer groove by a first predetermined distance, and the peripheral wall of the inner groove is separated from the peripheral wall of the outer groove by a second predetermined distance, and the first predetermined distance is The ratio of the second predetermined distance is 1:2.

Further, the inner tank is used to collect electrode corrosion generated when the electrode assembly is subjected to an electrochemical reaction.

Further, the outer tank has a first water inlet and a first water outlet, the collecting unit has a second water inlet and a second water outlet, and the circulating conveying unit comprises a first water inlet connected to the first water inlet a first direction conveying pipe between the second water outlet, a second direction conveying pipe connected between the first water outlet and the second water inlet, and a circulation connected to the second direction conveying pipe Pump.

Further, the first direction conveying pipe and the second direction conveying pipe are each Peristaltic hose, the circulation pump is a creeping pump.

Further, the distance between the first water outlet and the first water inlet is from 1:5 to 5.5, and the second water inlet and the second water outlet are respectively separated from the bottom of the collecting unit. The distance ratio is 1:5~5.5.

Further, the position of the first water inlet is higher than the position of the top of the inner tank, and the position of the first water outlet is lower than the position of the bottom of the inner tank.

Further, the electrode assembly includes an anode electrode and a cathode electrode disposed opposite to each other, and the anode electrode is a magnesium alloy electrode, and the cathode electrode is a graphite electrode.

Further, the disturbance unit is a magnet stirring device or a sound wave oscillating device.

Further, the disturbance unit is disposed at a groove bottom or a peripheral wall of the outer groove.

The invention has the beneficial effects of the system for separating and recovering struvite from sewage by the technical solution of the present invention, wherein the electrochemical reaction unit comprises a double-layer reaction tank and an electrode assembly, wherein the electrode assembly can be double-layered Electrochemical reaction in the inner tank of the reaction tank, and the formation of the solid product of struvite in the outer tank of the double-layer reaction tank" and the technical feature of "the collecting unit is connected to the outer tank of the double-layer reaction tank through a circulation conveying unit" In the reaction stage, the struvite solid product can be effectively separated from the electrode corrosion to improve the purity of the product, and no additional separation treatment is required thereafter.

For a better understanding of the features and technical aspects of the present invention, reference should be made to the accompanying drawings.

Z‧‧‧ system

1‧‧‧Electrochemical Reaction Unit

11‧‧‧Double reaction tank

111‧‧‧Inner slot

112‧‧‧ outer trough

1121‧‧‧first water inlet

1122‧‧‧ first outlet

12‧‧‧electrode assembly

121‧‧‧Anode electrode

122‧‧‧Cathode electrode

2‧‧‧ disturbance unit

3‧‧‧Circular conveyor unit

31‧‧‧First direction duct

32‧‧‧Second direction duct

33‧‧‧Circular pump

4‧‧‧Collection unit

41‧‧‧Second water inlet

42‧‧‧Second outlet

L1‧‧‧first predetermined distance

L2‧‧‧second predetermined distance

1 is a block diagram of a system for separating and recovering struvite from sewage according to the present invention.

Figure 2 shows a scanning electron micrograph of recovered struvite and commercial struvite according to the present invention.

3 is a compositional analysis diagram of recovered struvite and commercial struvite according to the present invention.

Figure 4 is a graph showing the purity of struvite as a function of reaction time.

Since the phosphorus resources on the earth are unevenly distributed and are gradually depleted, the present invention proposes a system for separating and recovering struvite from sewage, taking into consideration the recycling of phosphorus resources and the prevention of water pollution. The following is a description of an embodiment of the present invention relating to "a system for separating and recovering struvite from sewage" by a specific embodiment, and those skilled in the art can understand the advantages and effects of the present invention from the disclosure of the present specification. The present invention may be carried out or applied in various other specific embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention. In addition, the drawings of the present invention are merely illustrative and are not intended to be stated in the actual size. The following embodiments will further explain the related technical content of the present invention, but the disclosure is not intended to limit the scope of the present invention.

Please refer to FIG. 1 , which is a schematic diagram of a system for separating and recovering struvite from sewage according to a preferred embodiment of the present invention. The system Z comprises an electrochemical reaction unit 1, a disturbance unit 2, a circulation conveyor unit 3 and a collection unit 4. The electrochemical reaction unit 1 can separate the struvite from the sewage to be treated by electrochemical precipitation. The "sewage" mentioned here can be industrial factory, food factory, domestic sewage, or landfill. Phosphorus and nitrogen-rich organic sewage generated at the site is not limited thereto. The disturbance unit 2 keeps the sewage turbulent to prevent precipitation of the struvite. The circulation conveying unit 3 can circulate the sewage between the electrochemical reaction unit 1 and the collecting unit 4, and the struvite can directly settle to the collecting unit 4 due to gravity.

In the present embodiment, the electrochemical reaction unit 1 includes a double reaction tank 11 and an electrode assembly 12. The double-layer reaction tank 11 includes an inner tank 111 and an outer tank 112 surrounding the inner tank 111. The inner tank 111 and the outer tank 112 are both rectangular. The bottom groove of the inner tank 111 is spaced apart from the bottom of the outer tank 112 by a predetermined distance L1. The peripheral wall of the inner groove 111 and the peripheral wall of the outer groove 112 are also separated by a predetermined distance L2, and the ratio of the predetermined distance L1 to the predetermined distance L2 may preferably be 1:2, but is not limited thereto.

The electrode assembly 12 includes an anode electrode 121 and a cathode electrode 122. The anode electrode 121 and the cathode electrode 122 each include a reaction portion and a non-reaction portion, wherein the non-reaction portion is fixed on the outer groove 112, and the reaction portion is The top of the outer groove 112 extends into the inner groove 111. The anode electrode 121 may be a magnesium alloy electrode, and is preferably made of magnesium alloy scrap (such as AZ91D magnesium alloy die-casting waste) to achieve full use of waste and reduce cost, and the cathode electrode 122 may be a graphite electrode. .

It should be noted that when the double-layer reaction tank 11 contains sewage, the electrode assembly 12 can electrochemically react in the space in the inner tank 111, and the struvite solid product generated in the reaction can be made up of a large number of tiny bubbles. The air floatation flows out to the outer tank 112, and the electrode corrosion generated by the reaction can be collected by the inner tank 111. In this way, the struvite solid product can be effectively separated from the electrode corrosive during the reaction stage to improve the purity of the product, and no additional separation treatment is required thereafter.

In practice, a detection unit (not shown) may be disposed in the inner tank 111 for detecting the water quality condition and environmental conditions of the sewage to be treated. The detecting unit may include a plurality of different kinds of sensing elements, such as a temperature sensor, a pH sensor, a concentration sensor, etc., the temperature sensor can measure the temperature of the water, and the pH sensor can The pH value of the water is measured, and the concentration sensor can measure the concentration of nitrogen and phosphorus in the water. However, the type of the sensing element included in the detecting unit is not limited thereto.

The disturbance unit 2 may be a magnet stirring device and disposed at the bottom of the groove of the outer tank 112 to control the rotation of the magnet by magnetic force during the reaction, and the rotation speed may be adjusted according to the design of the tank body, for example, the rotation speed may be between 300 rpm and 900 rpm. In between, the sewage in the outer tank 112 is disturbed. Alternatively, the disturbance unit 2 may include one or more acoustic wave oscillating devices and may be disposed at the bottom or peripheral wall of the outer tank 112 to disturb the sewage in the outer tank 112 by sound wave oscillation of an appropriate frequency in the reaction. However, the type of the disturbance unit 2 is not limited to this.

The collecting unit 4 is connected to the electrochemical reaction unit 1 by the circulation conveying unit 3, that is, the circulation conveying unit 3 is formed between the electrochemical reaction unit 1 and the collecting unit 4. Into a loop. Specifically, the outer tank 112 has a first water inlet 1121 and a first water outlet 1122, wherein the position of the first water inlet 1121 is higher than the opening position of the tank top 111, and the position of the first water outlet 1122 is lower than The bottom position of the inner groove 111. The collecting unit 4 can be a collecting tank and has a second water inlet 41 and a second water outlet 42, wherein the second water outlet 42 is located higher than the second water inlet 41. The circulation conveying unit 3 includes a first direction conveying pipe 31, a second direction conveying pipe 32, and a circulation pump 33, wherein the first direction conveying pipe 31 is connected between the first water inlet port 1121 and the second water outlet port 42, The second direction conveying pipe 32 is connected between the first water outlet 1122 and the second water inlet 41, and the circulation pump 33 is connected to the second direction conveying pipe 32 for the first and second direction conveying pipes 31, The flow of sewage in 32 is reversed.

In practice, the first direction conveying pipe 31 and the second direction conveying pipe 32 may each be a peristaltic hose, and the circulation pump 33 may be a creeping pump, but is not limited thereto. In addition, the ratio of the distance between the first water outlet 1122 and the first water inlet 1121 from the bottom of the outer tank 112 may be 1:5 to 5.5, and the distance between the second water inlet 41 and the second water outlet 42 respectively from the bottom of the collecting unit 4 The ratio may be 1:5 to 5.5, but is not limited thereto.

Please refer to FIG. 2 and FIG. 3 . FIG. 2 shows scanning electron microscope (SEM) photographs of recovered struvite and commercial struvite according to the present invention, and FIG. 3 is a diagram of recovered struvite and commercial struvite according to the present invention. Component analysis chart. As shown in the above figure, the struvite recovered from the sewage by the system Z has a similar crystal structure and composition ratio with the commercial struvite. It can be proved that the system Z can fully recover phosphorus from the sewage. Nitrogen resources can further recycle phosphorus and nitrogen resources.

Please refer to FIG. 4 again, which is a comparative example of the experimental example using the system Z and the electrochemical reaction of the single-layer reaction tank under the same structure, under the same conditions (such as temperature, pressure and disturbance parameters). The struvite was recovered from the sewage, and the reaction time and the purity of the struvite were recorded. The results show that the system utilizes a two-layer reaction tank in the reaction stage, and separates the solid product of struvite from the electrode corrosion by the difference in specific gravity, which is very helpful for increasing the product concentration.

[Advantageous Effects of Embodiments]

The invention has the beneficial effects of the system for separating and recovering struvite from sewage by the embodiment of the present invention, wherein the electrochemical reaction unit comprises a double-layer reaction tank and an electrode assembly, wherein the electrode assembly can be double-layered Electrochemical reaction in the inner tank of the reaction tank, and the formation of the solid product of struvite in the outer tank of the double-layer reaction tank" and the technical feature of "the collecting unit is connected to the outer tank of the double-layer reaction tank through a circulation conveying unit" In the reaction stage, the struvite solid product can be effectively separated from the electrode corrosion to improve the purity of the product, and no additional separation treatment is required thereafter.

As described above, the system can use an anode electrode made of magnesium alloy scrap (such as AZ91D magnesium alloy die-casting waste) to carry out the reaction, so as to fully utilize the waste and reduce the cost.

Furthermore, the struvite recovered from the sewage by the system has a similar crystal structure and composition ratio to the commercial struvite, so that it can be directly used, eliminating the problem of subsequent processing.

The above disclosure is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Therefore, any equivalent technical changes made by using the present specification and the contents of the drawings are included in the application of the present invention. Within the scope of the patent.

Claims (10)

A system for separating and recovering struvite from sewage, comprising: an electrochemical reaction unit comprising a double-layer reaction tank and an electrode assembly, the double-layer reaction tank comprising an inner tank and an outer tank surrounding the inner tank, And the electrode assembly is disposed in the inner tank, wherein when the double-layer reaction tank contains sewage, the electrode assembly can perform an electrochemical reaction in the inner tank, and a struvite solid product generated in the electrochemical reaction It can flow out to the outer tank by air flotation of a large number of tiny bubbles, and an electrode corrosive material generated by the electrochemical reaction can be collected by the inner tank; a disturbance unit disposed at the bottom or the peripheral wall of the outer tank Means for disturbing the sewage in the outer tank to prevent precipitation of the struvite solid product; and a collecting unit interconnected with the outer tank through a circulation conveying unit, wherein the circulating conveying unit is used for the sewage Circulating flow between the electrochemical reaction unit and the collection unit, and allowing the struvite solid product to settle in the collection unit. The system for separating and recovering struvite from sewage according to claim 1, wherein a bottom of the inner tank is spaced apart from a bottom of the outer tank by a first predetermined distance, and a peripheral wall of the inner tank and the outer tank The peripheral wall is separated by a second predetermined distance, and the ratio of the first predetermined distance to the second predetermined distance is 1:2. A system for separating and recovering struvite from sewage according to claim 1, wherein the inner tank is used to collect electrode corrosion generated when the electrode assembly is subjected to an electrochemical reaction. The system for separating and recovering struvite from sewage according to claim 1, wherein the outer tank has a first water inlet and a first water outlet, and the collecting unit has a second water inlet and a second water outlet. a nozzle, the circulation conveying unit includes a first direction conveying pipe connected between the first water inlet and the second water outlet, and a second direction connected between the first water outlet and the second water inlet Duct and a circulation pump connected to the second direction conveying pipe. The system for separating and recovering struvite from sewage according to claim 4, wherein the first direction conveying pipe and the second direction conveying pipe are each a peristaltic hose, and the circulation pump is a peristaltic pump. The system for separating and recovering struvite from sewage according to claim 4, wherein a distance ratio between the first water outlet and the first water inlet is from 1:5 to 5.5, the first The ratio of the distance between the two water inlets and the second water outlet from the bottom of the collecting unit is 1:5 to 5.5. The system for separating and recovering struvite from sewage according to claim 6, wherein the position of the first water inlet is higher than the position of the top of the inner tank, and the position of the first water outlet is lower than that of the inner tank The bottom of the groove. The system for separating and recovering struvite from sewage according to claim 1, wherein the electrode assembly comprises an anode electrode and a cathode electrode disposed oppositely, the anode electrode is a magnesium alloy electrode, and the cathode electrode is a graphite electrode. The system for separating and recovering struvite from sewage according to claim 1, wherein the disturbance unit is a magnet stirring device or a sound wave oscillating device. A system for separating and recovering struvite from sewage according to claim 9, wherein the disturbance unit is disposed at a bottom or a peripheral wall of the outer tank.